This invention relates to computer based process monitoring systems for use in various manufacturing operations. The invention particularly relates to such systems which seek to apply statistical process control analysis to multiparameter manufacturing operations on a continuous basis with contemporaneous reporting of the results in human readable form.
The manufacture of all goods includes at least one step or process by which material of a first composition and configuration is modified to assume a second configuration and/or composition. Each such step or process involves the application to the first material of one or more forces, or the addition or subtraction of matter or energy to arrive at the second. Generally, the manufacturing processes are very complex with dozens, if not hundreds or even thousands, of individual elemental process being applied to an initial set of materials to ultimately form a final product. For example, a given product may achieve an intermediate stage or its final form by the individual elemental process of heating a body of material for a specific period of time or drilling a hole in a body of material of a specific size to a specific depth.
Where overall product uniformity is desirable, each of the individual elemental processes is preferably keep as uniform as possible. Contemporary quality control theory recognizes that some variation in each individual elemental process will occur and that some tolerances must be provided which define whether a product is considered acceptable. The permissible variation in some individual elemental processes can be relatively large while in others the variation must be very small. It is additionally recognized that the variations within the individual elemental processes can be subjected to a statistical analysis. Such analysis can identify those processes in which a non-random variation is occurring and distinguish variation occurring due to an un-correctable cause such as naturally expected variation in material density or the like. It is assumed that any non-random variation is due to a correctable cause such as a worn or loose tool, an out of sync timer, or the like.
In order to monitor a selected individual elemental process it is merely necessary to identify one or more measurable values or attributes directly associated with the successful completion of that individual elemental process, for example, the depth, diameter, and angle relative to a surface of a whole which has been drilled, or the color of the surface surrounding that hole. Appropriate gauges are adopted for each measurable characteristic and applied to the stream of goods subsequent to the process in question. Appropriate sampling of the stream of goods will give sufficient information to permit the application of statistical analysis in some situations. If the sampling is increased appropriately, the statistical analysis tends to give more accurate and more timely identification of variations occurring is due to correctable causes. The ultimate analysis is achieved by applying the gauges to all of the goods resulting from the process rather than merely a sampling. As a practical matter, manual gauging and statistical analysis of the results is usually not possible due to the significant demands on manpower and resulting time delays effectively slowing the manufacturing process.
Computers have been called on to assist in this measurement and assessment of process variables. A given stream of goods may be subjected to specific gauging operations with the aid of computer controlled robots which manipulate gauges and each workpiece in the same way each time to take any number of selected measurements. Additional gauges can be applied to the apparatus carrying out the manufacturing process so as to reflect the process parameters themselves rather than a product attribute. The output of each gauge which reflects a measurement taken may then be fed into a data base of the same or, more likely, another computer along with an identification of the selected measurement, commonly called a tag. The data base may then be subjected to selected programs intended to provide the numerical analysis concerning the many parameters in the process leading to the stream of goods. The output of such programs is desirably expressed in a humanly perceivable form such as control charts and production record tables, or even video displays, which can then be scanned by the persons responsible for the manufacturing process. Upon the identification of a problem as reflected in the control charts, production record tables, etc., corrective action can be taken.
While this is a vast improvement over any manual operation, there often is very little time available to production personnel to review and interpret the control charts, production record tables, etc., so that timely corrective action can be taken. This is particularly true where a large number of individual elemental processes are being monitored, each of which is capable of causing a computer to generate control charts and production record tables. In such a situation, the production personnel are faced with the substantial problem of even identifying which of the many control charts, production record tables, etc., should be examined for possible problem identification. This leads to time delays in process error identification, and related delays in process correction, thus leading to significant amounts of non-compliant goods.
Thus, the central problem sought to be solved by the present invention is a real-time identification of any process which requires prompt human attention, and if necessary intervention. That is, out of the hundreds or even thousands of variable parameters in a given manufacturing process, only a handfull deserve human attention at any given instant in time. The remaining process parameters are behaving in a normal manner and human review of such normally behaving parameters is unlikely to result in any significant process or product improvement. Thus, an object of the present invention is the computer-aided identification of any process parameter in a multiparameter manufacturing process requiring attention. Another object of the present invention is the communication of such computer-aided identification in a manner which will elicit a prompt human evaluation of the problem identified to permit timely intervention in the manufacturing process, if warranted.